The pathogen that triggered the Irish potato famine in the 1840s probably originated in central Mexico, not in the Andes, as some studies had suggested.

A genetic analysis of the pathogen, Phytophthora infestans, and its closest known relatives suggest that the microbes found in the Andes are descendants of the Mexican-based pathogens, scientists report June 2 in the Proceedings of the National Academy of Sciences.

The finding appears to resolve the debate over two competing theories of where the microbe came from and could help with efforts to develop crops that are resistant to P. infestans infestations.